Manually actuated positioning device with high resolution and large range of motion

ABSTRACT

A linear stage having a screw-nut assembly is actuated by the rotational motion of the screw. A mechanism, which is an integral part of the nut, quickly disconnects the screw and the nut, allowing rapid positioning of the linear stage in both the forward and reverse direction. The motion of said stage has a resolution given by the thread pitch of the screw and the nut; and a travel only limited by the length of the screw. The quick disconnect screw-nut assembly mechanism described in this invention is achieved by axial preloading said nut and allowing said nut to pivot perpendicular to the axis of said screw. Two or more linear stages having said screw-nut assembly are concatenated with one another to form a multi-axis positioning device.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] Provisional Patent Application No.: 60/434,301

STATEMENT REGARDING FEDERALY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not Applicable

REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTINGCOMPACT DISK APPENDIX

[0003] Not Applicable

BACKGROUND OF THE INVENTION

[0004] 1. Field of the Invention

[0005] The present invention relates to (i) positioning devices and moreparticularly to manually actuated linear stages; and to (ii)anti-backlash screw-nut assembly mechanisms generally used inpositioning devices.

[0006] 2. Description of the Relevant Art

[0007] In a linear stage two plates slide parallel and opposite to oneanother. If a screw and nut assembly connects the two plates of saidlinear stage, the rotation of the screw generates a rectilinear motion.There is always a tradeoff between the resolution and the total travelof a linear stage, particularly when it is manually operated. Forinstance, for a screw with a thread pitch of 0.050 inches (1.27 mm), asin a ¼″-20 ACME thread lead-screw, a 5 degree rotation translates into alinear motion of approximately 0.0007 inches (0.0176 mm or 17.6microns). Using the same lead-screw, it takes 200 full turns orrevolutions to move the stage 10 inches (254 mm). This is inconvenientwhen high resolution and fast motion are required in manually operatedsingle or multi axis positioning devices. However, this limitation canbe overcome by temporally disconnecting the threads of the nut and thescrew, leaving the linear stage free to be rapidly positioned, and then,re-connecting the threads of the nut and the screw to resume the linearstage high resolution motion.

SUMMARY OF THE INVENTION

[0008] The present invention relates to a linear stage having ascrew-nut assembly which comprises a nut-housing, a nut and a screw. Thenut is connected to one plate of the stage through the nut-housing. Theinternal thread of the nut mates with the external thread of the screw,which is attached to the other plate of the stage. In thisconfiguration, a rotation of the screw results in a rectilinear motion,and said motion has a resolution given by the thread pitch of the screwand the nut, and a travel limited by the length of the screw. The nut inthe screw-nut assembly has a partial thread and a contiguous roundexcision; and said nut is held in the nut-housing so it pivotsperpendicular to the axis of the screw. In addition, said nut is radialand axial preloaded with respect to the screw, to eliminate backlash.

[0009] The internal thread of the nut and the external thread of thescrew are disconnected by manually overcoming the radial preload on thenut, and the stage can be rapidly repositioned by the operator. Byreleasing the nut, the screw and nut threads connect and the stage canthen be moved by turning the screw.

[0010] A plurality of linear stages concatenated with one another toform a multi-axis positioning device. Said multi-axis positioning devicehaving linear stages with angle adjustable bases, micrometer resolutionand rapid displacement via a quick disconnect nut mechanism as describedin the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a top view, side view and bottom view of a linear stagewith a quick-disconnect, anti-backlash screw-nut assembly as describedin the present invention.

[0012]FIG. 2 is a side sectional view of the screw-nut assembly shown inFIG. 1, depicting the pivoting point and radial preload on the nut,which enables the connection between the inner thread of the nut and theouter thread of the screw.

[0013]FIG. 3 is a side sectional view of the screw-nut assembly when aforce opposite to the radial preload is applied, which disconnects theinner thread of the nut and the outer thread of the screw.

[0014]FIG. 4 is a top sectional view of the screw-nut assembly shown inFIG. 1, to depict the axial preload on the nut.

[0015]FIG. 5 is a view of a multi-axis positioning device, composed of aplurality of linear stages as described in the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention relates to a linear stage having ananti-backlash screw-nut assembly which comprises a nut-housing 30, a nut40 and a screw 50. The nut is connected to one plate 10 of the stagethrough the nut-housing 30. The internal thread of the nut 40 mates withthe external thread of the screw 50, which is attached to the otherplate of the stage 20. In this configuration, a rotation of the screwresults in a rectilinear motion. In the case of the linear stage shownin FIG. 1, this is achieved by manually turning the knob 60, which isconnected to the screw 50.

[0017] As shown in FIGS. 2-4, the nut 40 is held in the nut-housing 30,such as said nut 40 pivots 43 perpendicular to the axis of the screw 50;and said nut 40 having an internal thread and a contiguous roundexcision, resulting in the partial removal of the internal thread 41.Said nut 40 having the center point of the imaginary circumferenceprojected by its partial internal thread in the same geometric planethan the pivoting point. In addition, by inserting compression springsbetween said nut 40 and nut-housing 30, said nut is radial 45 and axial46 preloaded with respect to the screw 50. The radial 45 preload allowsthe connection of the inner thread of the nut 40 and the outer thread ofthe screw 50. Also, the radial 45 preload on said nut 40 compensates forthe non-linearity and out of roundness of the screw 50 and eliminatesall possible play between the internal thread of the nut and theexternal thread of the screw. In addition, the axial 46 preload on saidnut 40 eliminates all possible play between the nut and the nut housing.If said nut 40 is fitted in the nut-housing 30 such as there is nopermissible axial play, but the pivoting motion of said nut 40 is stillallowed, only radial preloading 45 of said nut is required to connectthe nut 40 and the screw 50 and to eliminate backlash.

[0018] The internal thread of the nut 40 and the external thread of thescrew 50 are disconnected by overcoming the radial 45 preload on the nut40 (see 49 in FIGS. 2-3). Given that the cutout adjacent to the partialthread of said nut 40 is made bigger than the diameter of the screw,said nut 40 is free to move along the axis of the screw (see 41 FIG. 3),and the stage can be rapidly repositioned by the operator. By releasingsaid nut 40, the screw and nut threads connect and the stage linearmotion is then resumed by turning the knob 60 connected to the screw 50.

[0019]FIG. 5 shows a plurality of linear stages 70, 80, 90 concatenatedwith one another to form a multi-axis positioning device. Saidmulti-axis positioning device having linear stages with angle adjustablebases 90, micrometer resolution and rapid displacement via a quickdisconnect anti-backlash nut mechanism as described in the presentinvention. For simplicity, the description of the invention is limitedto a rectilinear motion. However, the invention is extended to anytranslational movement along the screw which is generated by therotation of the screw relative to a moving part coupled to said screwvia a nut. Said screw rotation being manual or motor driven. Also, theinvention is extended to full thread nuts, in which radial and axialpreloading in addition to pivoting, are used to effectively eliminatebacklash.

[0020] While this invention has been particularly shown and describedwith references to preferred embodiments thereof, it will be understoodby those knowledgeable in the art that several changes in form anddetails may be made therein without departing from the scope of theinvention.

I claim:
 1. A linear stage comprising: a screw-nut assembly connectingthe opposite sliding plates, in which the rotational motion of the screwtranslates into a rectilinear motion; said screw-nut assembly having inaddition to the screw, a nut-housing and a nut; said nut connected tothe nut-housing and let to pivot perpendicular to the axis of the screw;said nut having an internal thread and a contiguous round excision,resulting in the partial removal of the internal thread; and said nuthaving the center point of the imaginary circumference projected by thepartial internal thread in the same geometric plane than the pivotingpoint; and compression springs inserted between the nut and thenut-housing, for producing a radial preload and an axial preload on saidnut with respect to the screw; and said radial preload for engaging theinternal thread of the nut and the external thread of the screw and foreliminating any play between the inner thread of the nut and the outerthread of the screw; and said axial preload for eliminating any playbetween the nut and the nut-housing.
 2. A linear stage as recited inclaim 1 wherein the rotational motion of the screw is manual or motordriven.
 3. A screw-nut assembly as recited in claim 1 wherein there isno permissible axial play between said nut and said nut-housing; saidnut having only radial preload to connect the inner threads of the nutand outer threads of the screw and to eliminate backlash.
 4. A screw-nutassembly as recited in claims 1 and 2, having a nut with a full internalthread.
 5. A screw-nut assembly as recited in claim 1 wherein a forcegreater an opposite to the radial preload is applied on said nut,resulting in the disconnection of the inner thread of the nut and theouter thread of the screw, and freeing the sliding plates of the stageas recited in claim 1, to generate a rectilinear motion withoutrequiring the rotational motion of the screw.
 6. A screw-nut assembly asrecited in claim 4 wherein the force greater an opposite to the radialpreload being applied on said nut is removed, resulting in theengagement of the internal thread of the nut and the external thread ofthe screw, and enabling the rotational motion of the screw to betranslated into a rectilinear motion.
 7. A plurality of linear stages asrecited in claim 1 concatenated with one another forming a multi-axispositioning device; said multi-axis positioning device having screw-nutassemblies as recited in claims 1, 2, 3, 4, 5 and 6.